 Assalamu alaikum. In this lecture, we are going to talk about reproduction, reproductive systems as we know that the living organisms have certain specific properties which make them living organisms. One of these properties is to acquire energy from the environment, acquire food from the environment for getting energy and continuing with the life processes. The other most important property is that they reproduce themselves, they produce their offsprings, their young ones who are valid enough, who are strong enough to get energy from the environment and reproduce on themselves. That is producing valid offsprings is a property of life, one of the most important properties of life. We call any organism anything living if it acquires energy from the environment and it reproduces and it changes itself according to the environment. Although reproduction is a property, a characteristic of the living organism, the life, what is reproduction? This is a biological process by which the organisms produce their offsprings, their young ones which are similar to their parents. In some cases they are absolutely same, in many other cases they are similar but have many new properties. This ability allows the organisms, number one, to continue their race and number two, to adapt itself to the changing environment. The new organism which have some newer properties may be better adapted to the environment in which organism is living, sometimes it have some harmful properties, some other properties which are not useful, rather harmful then this organism have a decreased rate of survival and after a long period of time, if this harmful characteristic is there and maybe it is increasing, this may lead towards extinction of that animal group. But mostly what happen, the characteristics they improve, if they improve the organism will continue its race, if they do not or if some we can say bad characteristics they appear then organism may become extinct. Now, the types of reproduction, there are two main types of reproduction, one is called asexual and other is called asexual, asexual means that in that is production of the offsprings by a simple cell division and by a single parent, so in asexual reproduction only one parent cell can produce offsprings and they can produce offsprings by simple cell division, these offsprings are exact copies of their parents, they are absolutely same because there are no changes in their DNA, in their genetic material, as we know that the mitosis or the simple cell division, it divides a cell into two daughter cells which have identical set of genes and we know that genes are the components of living organisms, the genetic material which actually makes all the characteristics, the traits of a living organism, we know that genes makes proteins and proteins are structural or functional, structural then they make structures of the living organism, they are functional when they perform different types of functions, for example like enzymes which catalyzes different types of reactions in the body of the organisms, so if genes are same the characteristics of the organism are same, so in asexual form of reproduction because the daughter cells, the offsprings or the young ones are the exact genetic copy of their parents, they have exact same characteristics, this type of reproduction actually have a disadvantage that is because the offsprings are exact copies of their parents, they do not have some new properties, they are not better adaptable to environment, there are no new combinations possible, so these organisms have a disadvantage and this is considered as a primitive or an old form of reproduction, though there are lot many organisms which carry out this asexual reproduction, but most of the organisms which are better or more adapted, they adopted the other form which is called sexual reproduction, sexual reproduction is that two organisms are involved in producing offsprings, one is conventionally called a male and other is conventionally called female, but in some other organism both type of organs are present in the same organism, the male parts and the female parts both are present in the same organism, but we call them bisexual, most of the organisms they are called unisactual that is in one organism only one types of parts are present either male or a female, what is the difference because the males and females they make some specific cells called gametes, these gametes have to fuse to make a new organism, we call this process fertilization, what is the advantage one cell is coming from one organism, another cell is coming from another organism when they fuse they result in some new combinations, because one organism have some different characteristics, the other organism have some different characteristics, when these characteristics join that is these genes join they make some new combinations or some new characteristics, the result is this that the organism is better adapted to the changes in the environment which are occurring naturally all the time, so sexual reproduction is present in more advanced forms of life, in plants in animals in all the larger animals they reproduce sexually that is by involvement of gametes and by involvement of male and female that is two organisms, there is a second advantage the gametes the germ cells these are produced by a process called meiosis rather than mitosis, meiosis is a process in which when the cell is dividing its genetic material go through some new combinations, we call it genetic recombination, when there is a first phase pro phase of meiosis there are lot many genetic recombinations which takes place in the genetic material, so the resulting cell the germ cell or the gamete, the gamete actually is a more adaptable cell that is it have some new genetic recombination. So, there are two advantages number one genetic recombination is coming from the meiosis process in the single organism in the single gamete and when the gametes from two organisms the fuse they add actually even more combinations of genetic material, the result is as we know if genetic material have more combinations the characteristics of organism which are the result of that genetic recombination are much more in the organism become more adapted to the current environment and to the changing environment. So, most of the higher organisms they have sexual reproduction and some of the particularly plots they have in their life sometimes both of these types of reproduction that is sometimes asexual and sometimes sexual. So, we talk about these both of these forms of reproduction one by one.